Macroalgae Photosystems and Dark Periods

[pjf]

Will someone please supply me with links to the following information about Photosystems I and II?

• Macroalgae that can be placed under lighting 24 hours a day, such as caulerpa, use which photosystem?
• Which photosystem requires a “dark” period and why?
• Which light spectrum is preferred by which photosystem?
• Which photosystem predominates in refugium macro-algae (caulerpa, chaetomorpha, gracilaria, etc.) used for natural nitrate reduction?

Thanks!

[jrhupp]

PSI shows peak absorbtion around 700nm, and PSII shows peak absorbtion around 680nm. Most plants utilize both photosystems, this holds ture for the major divisions of alge we keep; Chlorophyta, Rhodophyta and Phaeophyta. Although in the later two I belive other photosynthetic pigments are common as well (xanthophylls? and...???). Neither photosystem requires a "dark" period (I think this missconception comes from high school biology text reffering to the "dark reactions" and describing them as photosynthesis running in reverse). But few plants benifit from constant illumination. I belive this has more to do with disruption of other (eg non-photosynthesis related) meatabolic pathways that are light mediated (eg respond to presence/absence, type of light...), than anything directly related to photosynthesis.

Hope it helps,
Jay

[pjf]

Thanks for the information!

I am illuminating the chaetomorpha in my refugium for 12 hours each night with a "reverse daylight photosynthesis" (RDP) protocol. In the near future, I may be replacing the green chaetomorpha with red gracilaria parvispora.

What light spectrum should I use to illuminate the chaetomorpha or gracilaria? I want to replace my power compact fluorescent bulb. The choices include:
• Actinic
• Daylight
• ½ Actinic & ½ Daylight
• ½ Red & ½ Daylight
(http://www.customaquatic.com/customaquatic/subsubcategorypage.asp?subcatindexid=lt-rpcb-13)

I’d appreciate it if you could very briefly explain your bulb choice. I am confused by the seemingly contradictory absorption spectra of chlorophyll-a, chlorophyll-b, Photosystem I, Photosystem II, green algae, red algae, and, of course, accessory pigments. If you are busy, a link to more information would be appreciated.

Thanks!